1. Field of the Invention
This invention relates to magnetic transducers particularly applicable to magnetic disk drive systems. More particularly, the invention relates to thin film inductive heads having a reduced profile to improve track definition and heat dissipation.
2. Description of the Related Art
Thin film magnetic read/write heads are used for reading and writing magnetically coded data stored on a magnetic storage medium such as a magnetic disk or a magnetic tape. There is a continuing strongly-felt need for increasing the data storage density in such media. Most efforts to increase magnetic storage density involve techniques for increasing the areal bit density in the magnetic medium.
In rotating magnetic disk drives, the areal density is the product of the number of flux reversals per millimeter along a data track and the number of tracks available per millimeter of disk radius. Thus, high areal data storage density requires recording heads with high linear resolution and narrow track width.
A thin film inductive write head includes one or more coil layers imbedded in an insulation stack, the insulation stack being sandwiched between first and second pole piece layers. A write gap is formed in a pole tip region by provision of a gap layer between the pole pieces. The pole pieces are magnetically coupled in a back region. Between the pole tip region and the back gap region is a yoke region where the pole piece layers separate from one another to accomodate the insulation stack. The insulation stack typically includes a first insulation layer (I1) on the first pole piece layer, one or more coil layers on the first insulation layer, a second insulation layer (I2) over the coil layer and a third insulation layer (I3) over the second insulation layer.
A combined head, such as a merged magnetoresistive (MR) head, includes the aforementioned write head as a write head portion combined with an MR read head portion. The MR read head portion includes an MR sensor which is sandwiched between first and second gap layers which are in turn sandwiched between first and second shield layers. In a merged MR head, a single layer serves a double function as a second shield layer for the read head and as a first pole piece for the write head. The combined head is carried on a slider which, in turn, is mounted on a suspension in a magnetic disk drive. The suspension is mounted on an actuator which moves the combined head over selected tracks on a rotating disk for reading and writing signals thereon. As disk rotates a cushion of air is developed to provide an air bearing between the disk and the slider which counterbalances a loading force exerted by the suspension. A surface of the slider facing the disk is called an air bearing surface (ABS) and is typically spaced from the disk in the order of 0.050 xcexcm when the disk is rotating.
In the fabrication of a thin film magnetic write head it is important that zero throat height (ZTH) be accurately located. The ZTH is the distance along a normal to the ABS between the ABS and a first location where the first and second pole piece layers separate due to topography of one of the insulation layers in the aforementioned insulation stack. Typically an apex of the first insulation layer defines the ZTH. The apex is the foremost end of the insulation layer closest to the ABS. The first insulation layer is hard baked resist which imposes on the layer an upwardly sloping surface which commences at the apex forming an apex angle with the plane of the write gap layer. Accordingly, the sloping surface of the first insulation layer angles toward the second pole piece, causing an angled separation of the first and second pole piece layers which commences at the apex. The apex angles of the first, second and third insulation layers cause pronounced slopes which rise from the ZTH and face the pole tip region. After hard baking these layers high optical reflectivity presents a problem in the fabrication of the second pole tip.
For good magnetic operation, it is desirable that the sidewalls of the second pole tip be planar and perpendicular to the ABS. One approach is to make the tracks wider, however, this reduces the storage density of the disk. Therefore, in order to maintain high storage density, the art has endeavored to make the sidewalls of the pole tip regular. Two design considerations make this endeavor difficult. First, the first and second pole piece layers must separate as near as possible to the ABS in order to minimize flux transfer between the pole tips behind the ABS. This requires that the distance between the ABS and the ZTH be minimized. Second, the second pole piece should widen as near as possible to the ABS to minimize saturation of the second pole tip. This widening commences at the xe2x80x9cflare pointxe2x80x9d. The ZTH is typically located between the ABS and the flare point. When both the ZTH and the flare point are close to the ABS, the optical reflectivity of the front slope of the insulation stack presents a problem in the fabrication of the second pole tip.
The second pole tip is constructed by spinning a thick photoresist layer on top of the insulation stack, over the site of the second pole tip. Ultraviolet light is then directed onto the photoresist through a mask that outlines the shape of the second pole tip. In the prior art, the flare point is behind the ZTH, over the front sloping reflective surface of the insulation stack. That portion of the ultraviolet light which is directed behind the flare point is reflected from the front slope of the insulation stack, enlarging the exposure of the photoresist on each side of the intended sidewalls of the second pole tip. When the photoresist is developed, the photoresist mask at the second pole tip region may be undesirably wide. This undesirably widens the second pole tip which leads to its irregularity.
Another problem with the insulation stack is that the insulator layers formed of baked resist are relatively thick due to the spin coating process used to deposit the resist material. The baked resist is a relatively poor thermal conductor resulting in heating of the write head due slow dissipation of heat generated in the coil layer when the write head is operated.
A further problem with the insulation stack is its proximity to the ABS. Unfortunately, the coefficients of expansion of the materials of the insulation stack and the pole piece layers are markedly different. When the write head is operated the coil layers generate heat, which causes expansion of the insulation stack and pole pieces. The material of the insulation stack expands more than the alumina overcoat and the pole pieces causing the overcoat and the pole tips to protrude beyond the ABS of the slider. This same expansion of the insulation stack can also cause cracking at interface of the second pole and the write gap at the ABS.
Accordingly, there is a strong felt need to overcome or minimize the aforementioned problems associated with prior art inductive write heads.
It is an object of the present invention to disclose an inductive write head having a thinner insulator stack layer.
It is another object of the present invention to disclose an inductive write head having a reduced apex angle and a lower profile.
It is a further object of the present invention to disclose an inductive write head having a reduced yoke length.
It is yet another object of the present invention to disclose an inductive write head which does not exhibit a large overcoat and pole tip protrusion and cracking between layers due to expansion of the insulation stack.
It is still another object of the present invention to disclose an inductive write head using a thin insulator material for the first insulator layer of the insulator stack.
It is a still further object of the present invention to disclose a method for making an inductive write head having a reduced apex angle, a low profile, a thinner insulator stack and a reduced yoke length.
It is a still further object of the present invention to disclose an inductive write head having improved heat dissipation upon operation of the write coil.
In accordance with the principles of the present invention, there is disclosed an inductive write head having a first insulation layer of a coil insulation stack formed of aluminum oxide. Because of the good electrical insulative properties of aluminum oxide, the first insulator layer of the coil insulation stack can be made having a thickness in the range of 0.2-0.3 microns. This thin first insulator layer together with a reduced thickness second insulation layer results in a lower profile write head having a reduced apex angle and a reduced yoke length. The reduced yoke length is achieved by making the coil layer closer to the first pole piece (P1) due to the thinner first insulator layer so that the coil can be moved closer to the ABS without a detrimental effect on the apex angle.
The thin first insulator layer of aluminum oxide has good thermal conductance resulting in improved heat sinking of the coil layer of the write head reducing pole tip protrusion and cracking at the pole tip/write gap layer interface layer due to expansion of the insulation stack.